When designing a skin adhesive, one of the major issues is to keep the skin relatively dry underneath the adhesive so as to prevent maceration. Maceration occurs when the skin is unable to get rid of moisture from transpiration and results in degradation of the skin's barrier function as well as bad adhesion of the device to the skin.
Usually, skin adhesive keeps the skin dry by being moisture permeable. This allows moisture to transport through the adhesive from the skin side to the opposite side, where it is allowed to evaporate.
Adhesives for fastening a bodily waste collecting pouch or tube are usually covered by a moisture impermeable layer that does not allow moisture from the skin to permeate through the adhesive and out into the surroundings.
Therefore, adhesives for fastening a collecting pouch or tube are made moisture absorbent. Absorbing particles or hydrocolloids (HC) are mixed into an adhesive matrix in order to absorb moisture from the skin and thereby keeping the skin relatively dry. This technique is well known in the art and forms the basis for most commercially available ostomy adhesives see, e.g. U.S. Pat. No. 4,192,785.
The major problem in using an absorbing adhesive is that the bonding properties change as the adhesive absorbs moisture. What started out as being a well-bonded adhesive, usually ends up being a weak-bonded adhesive after absorbing moisture. This effect is particularly a problem for hydrocolloid-based adhesives. These adhesives comprise two phases, a hydrophobic matrix with hydrophilic hydrocolloids (HC) dispersed therein. As the adhesive absorbs moisture from the skin, the hydrocolloids swell and take up an increasing amount of space in the skin-bonding zone. It is the hydrophobic part of the adhesive that is responsible for the bonding to the skin and as the hydrophobic part is being “squeezed” out by the expanding hydrophilic domains, the skin bonding is reduced. There is further a risk that, if small drops of moisture, e.g. due to active perspiration (sweating) are formed between the skin and the adhesive, small parts of hydrocolloid can be washed out into the droplet and thus reducing bonding between the skin and the adhesive. This creates an area in the skin-adhesive interface where no new adhesive bond can be formed as the HC has no cohesive and adhesive power in it self. If there had been no HC present, the adhesion would be better but then there would be no absorbing capacity of the adhesive.
Hence, there is a need to isolate the absorbing part of the adhesive from the skin, and still maintain an ability to adhere and absorb moisture.
In AU 2004224963, a two-layered adhesive for ostomy and wound care applications is disclosed. The invention combines the mechanical effects of two layers of different hydrocolloid (HC) based adhesives. One layer close to the skin provides good initial tack while the other layer is ‘soft’ and provides good moisture resistance. The patent does not address the change in properties after moisture absorption in the layer. This moisture absorption is bound to be large if maceration of the skin is to be kept at arms length—The HO adhesive described in the patent is based on hydrophilic particles (HC) dispersed in a moisture impermeable matrix: Thus, moisture permeation can only be achieved through the particles. For moisture to permeate through the adhesive matrix, particles need to touch each other. To achieve sufficient moisture permeability, lots of particles need to touch each other and this can only be achieved by mixing in large amounts of particles. All of these particles will absorb moisture and the entire adhesive will significantly change properties when exposed to water. Further, the patent does not solve the problem of HC in the surface of the adhesive that can be washed out by active perspiration, destroying the ability of the adhesive to adhere to the skin.
In EP1679085, a skin adhesive is disclosed with very good water vapour permeability. This adhesive is in itself very low absorbing and is thus unsuitable for holding a pouch for collecting bodily waste because of the arguments mentioned above. However, because of the very good adhesive properties and the high permeability of the adhesive, it is suitable for a skin-facing layer as it does not change properties significantly when exposed to water. It can therefore be combined with an absorbing layer to yield an adhesive wafer suitable for use in attaching a pouch for collecting bodily waste.
In WO2007/092289, a number of ostomy devices containing several different layers are disclosed. A common feature of all these devices is that the skin-facing layer is liquid permeable, thus allowing liquid to transport from skin to a layer of absorbing material behind the skin facing layer. The device enclosed in the present invention, the skin-facing layer is liquid impermeable but moisture permeable. Even when the skin-facing layer only covers part of the absorbing layer, the absorbing layer is still liquid impermeable making the entire skin-facing surface liquid impermeable.
It has now surprisingly been found, that the layered construction according to the invention provides a collecting device comprising an adhesive wafer that maintains its adhesive properties even after considerable moisture absorption.